1. Field of the Invention
This invention generally relates to apparatus and method for forming an integral laid fibrous web from multiple fiberizable components, and to articles produced thereby. More specifically the invention relates to apparatus and method of such type for forming an integral laid fibrous web with generally discrete, homogeneous compositional zones therein, and to the article formed thereby having laterally extending contiguous zones of different composition.
2. Description of the Prior Art
In the general practice of forming nonwoven fibrous webs, the source material in the form of a fibrous sheet such as pulp sheet, or other fiberizable feed source, is introduced to a fiberizer, wherein the fiber source material is disintegrated, shredded, fiberized or otherwise separated to produce a product material in the form of discrete, individual fibers. The product fibers then are suitably conveyed, for example, by gravity flow, or more commonly, by air-entrainment in a flow stream, onto a foraminous forming surface which may, for example, comprise a wire or screen, e.g., a Fourdrinier wire. The forming surface is translated, or otherwise moved, such as by means of an endless conveyor belt assembly, during the deposition of fibers, to yield the laid fibrous web. The fibrous web article produced thereby has utility in numerous absorbent article applications, such as sanitary napkins and disposable diapers.
In various absorbent article applications, it is desirable to provide a multicomponent fibrous web having discrete zones of different composition. For example, in the case of disposable diapers, it is desirable in some instances to provide a higher basis weight of absorbent material in selected areas of the diaper, and accordingly, it has been common practice to superimpose sequential layers of material in such areas to provide increased thickness and higher absorbency. Further, in forming nonwoven webs of cellulosic fibers, such as in papermaking, it sometimes is desirable to provide different compositional zones in selected products to accomodate different associated treatment steps. For example, different pore size gradients may be formed on different portions of a sheet, or one section of the sheet may be embossed and another section printed.
In many such instances where it is desired to provide a nonwoven fibrous web with multiple discrete compositional zones, it is advantageous for reasons of structural integrity, or ease of manufacture or use, to provide the web as an integral laid structure, as opposed to providing constructions wherein discrete individual layers are superimposed or adhesively bonded to one another. The prior art has proposed various apparatus and methods for producing integral laid fibrous webs with different compositional zones ktherein, but such zones characteristically have been in thickness layers, as opposed to laterally adjacent zones of different composition. In those instances where the prior art has proposed means for forming an integral laid fibrous web with laterally varying composition, the compsitional zones are not discrete and homogeneous in form, but rather the composition varies, linearly or otherwise, across the surface of the web. It, therefore, would be a significant advance in the art to provide an integral laid fibrous web from multiple fiberizable components, which is characterized by generally discrete homogeneous compositional zones in the sheet, wherein the compositional zones are laterally contiguous to one another and have a substantially homogeneous composition throughout the thickness of the web associated with each such zone.
U.S. Pat. Nos. 3,848,589 and 3,975,222 to F. K. Mesek describe the production of an air-laid web by simultaneously feeding to an individualizing station (fiberizer) two continuous strips of compacted fibers, one strip being narrower than and lying along the longitudinal median of the other, with the individualized fibers then being deposited on a moving foraminous belt from an airstream. Longitudinal peaks are provided in the air-laid web by varying the rate of feed of the continuous strips to the individualizing station, to provide a web panel which is double contoured, i.e., centrally contoured in the transverse and longitudinal directions to produce a smooth peak on one major surface. The patent states at column 8, lines 3-10 that alternatively, such longitudinal contour may be imparted to the web by varying the speed of the laydown surface or by grinding fibers at one station to produce a continuous web with a transverse contour and then sequentially grinding selecting amounts of fibers at another station which are deposited on the continuous web to produce repetitive longitudinal contours.
U.S. Pat. No. 3,994,047 to C. A. Lee, et al., discloses the formation of a composite pad from fibers air-laid on a twin-wire machine. A pair of endless foraminous carriers are passed through a forming chamber wherein air-entrained fibers are directed between the carriers, to build up a web structure on each of such carriers. Each of the forming wires has a discrete flow section defining the associated layer of the composite, and the respective carriers converge to join the facing surfaces of the respective web layers to form the composite having a non-uniform cross-section. The formed article illustratively disclosed in the patent is a pad suitable for use in applications such as disposable diapers, comprising a first layer of hourglass shape, and a second layer of ovate shape, which is superimposed on the first layer to provide an increased absorptivity region for the composite article. The patent discloses the provision of fibers from divellicated webs of felted wood pulp, with the fiber source for each of the respective layers of the pad being of the same composition.
French Pat. No. 2,521,602 to Societe Dite Etablissements Ruby, discloses an apparatus for concurrently forming two or more continuous fibrous webs requiring different feed rates. Multiple lay-up drums are coaxially mounted in side-by-side relationship, but driven via speed reduction couplings from the same drive motor at differing speeds. The apparatus is stated to be useful for preparation of complementary layers of composite absorbent fabrics for application such as sanitary pads, diaper linings, etc., having layers of differing compaction. As shown in the drawings of this patent, a compressed layer is supplied at the same output rate as an uncompressed layer for continuous subsequent superposition of the respective layers to produce a composite fabric.
U.S. Pat. No. 3,857,657 to R. K. Teed discloses an apparatus for forming a laid fibrous web in the form of discrete spaced-apart pads on a foraminous forming surface. A wet-pressed pulp fiber sheet is fed into a stationary housing forming a generally enclosed chamber open at its bottom portion, through a slot in the housing. In the housing is mounted a fiberizing device comprising a generally cylindrically-shaped roll having teeth around its outer circumference. The cylindrical roll may be in the form of a plurality of cylindrical disks mounted in side-by-side relationship on a common support shaft, with teeth around the outer periphery or circumference of each of the constituent disks. The resulting discrete fibers travel from the upper portion of the housing onto the forming surface which is in the form of an endless conveyor belt comprising sequential spaced-apart arrays of openings, corresponding to the shape and size of the laid web product. A vacuum suction arrangement acts to impose vacuum suction on the forming surface to cause fiber deposition on the perforated portions thereof. Gas flow conduits are disposed at opposite ends of the forming surface as presented to the fiberizer, and a motor driven fan creates a positive airstream through the region above the forming surface, in turbulent flow, to cause the fiberized fibers to settle only on the perforated portions of the forming surface and to pick up and remove fiberized fibers settling in spaces between the groups of perforations for recirculation to the pad forming area in the lower portion of the chamber defined by the housing. In the disclosed apparatus the longitudinal axis of the cylindrical roll in the housing is aligned parallel with respect to the center line (longitudinal axis) of the forming surface associated therewith, so that the fiber sheet if fed into the housing for fiberization therein, in a direction generally perpendicular to the direction of translation of the foraminous forming surface.
U.S. Pat. No. 3,963,392 to P. K. Goyal discloses an apparatus and method for forming a multicomponent integral laid fibrous web. The apparatus includes plural pairs of spaced parallel, oppositely rotating fiberizers (toothed cylinders), each pair having a movable divider plate therebetween. High speed air-streams flowing past each individual fiberizer entrain the fibers and carry same to a mixing zone between the respective fiberizers to form combined streams, which thereafter enter a common mixing zone above the forming surface, as a composite stream. The divider plates between each pair of fiberizers in this system are adjustable from a range of positions, from a completely withdrawn to a fully downwardly extending position, whereby the degree of intermixing of the entrained fibers in the combined streams may be controlled. A divider plate is also disposed in adjustable relationship with respect to the common mixing zone, to control the degree to which the combined streams intermix in forming a composite stream at the forming surface. The forming surface may define multiple laydown zones associated with individual suction sources which may be independently adjusted to further vary the web formed on the forming surface. The various fiberizer cylinders in this system are oriented with their cylindrical axes perpendicular to the direction of translation of the forming surface.
FIGS. 3-6 in this patent disclose a number of relative configurations of the various divider plates, whereby the web may be laid with sequential layers across its thickness. The patent also discloses at column 9, lines 39-49 that if a fiber collector were disposed immediately below a mixing zone associated with one pair of fiberizing cylinders, having two distinct components fed thereto on either side of the divider plate, but with the divider plate in a fully retracted position, the resulting web would have a concentration of fibers of one component at one face in excess of the overall concentration of such fibers in the web, with the opposite face of the web having a concentration of the other fibers in excess of the overall concentration of such other fibers in the web, i.e., with the concentration of the first-mentioned fibers gradually and generally linearly diminishing from the respective "enriched" face of the web to its opposite face.
The Goyal patent states that the configuration and density of teeth of the fiberizer cylinder may vary with the specific materials being fiberized. For fiberization of pulp board, the fiberizer cylinder teeth may have a pitch of about 3/32-1/2 inch, a tooth height of about 3/32-1/2 inch, and a tooth angle of about -10.degree. to about +10.degree.. For fiberization of rayon in the form of a carded batt, the corresponding values are about 1/8-1/4 inch for tooth pitch, about 1/8-1/4 inch for tooth height, and about -10.degree. to about +20.degree. for tooth angle. The pulp fiberizer is driven at a rotational speed of 6000 rpm and the rayon fiberizer is driven at 3000 rpm.
U.S. Pat. No. 3,943,605 to E. D. Nystrand discloses an apparatus and method for forming a composite fluff article wherein symmetrically arranged hammermills are fed by separate pulp web rolls, with the resulting fiberized streams being deposited on separate endless wire assemblies. One such laid fibrous layer is removed from its wire by suction and placed with its wire side engaging a wrap sheet traveling beneath the wire on which the second fluff layer is formed. The second layer is removed from its wire by applying suction from beneath, through the wrap sheet and the overlying first layer, to deposit the second layer on the first in inverted relation, i.e., with the respective top surfaces of the sheets as formed being abuttingly mated to form a composite sheet.
U.S. Pat. No. 2,624,079 to T. C. Duvall discloses a system for manufacture of air-laid felts wherein an endless conveyor is disposed beneath a series of deposition chambers. In each chamber a nozzle from a side wall discharges fibers by gravity in a trajectory which provides build-up of thickness of the web, followed by passage of the web through compression rolls to provide a high density, uniform thichness product. It is disclosed at column 5, lines 41-48 of this patent that the disclosed arrangement is flexible, and permits different kinds of materials or different forming conditions to exist in the several chambers, which may be employed in such a way as to build up a symmetrical composite mat which is continuous, but has sequential layers corresponding to the respective deposition chambers. FIG. 3 of this patent shows a composite integral web having outer layers of high grade material such as bleached sulfite fibers, the inner layers being of coarse or unbleached fiber material. It is further disclosed that a bank of injection devices (discharge nozzles) may be provided cross-wise of the web to be formed, i.e., transverse to the direction of translation of the forming surface.
U.S. Pat. No. 2,751,962 discloses a system for producing fibrous products wherein coarse and fine fibers are concurrently incorporated into an integral web. Specifically described is a system for laying of glass fibers from a for hearth of a furnace. A series of orifices in a flow communication with the forehearth receive molten or flowable fiber-forming material and under the influence of downwardly directed blasts of superheated stream of air impinging thereupon, the molten glass material is drawn or attenuated into fibers which pass downwardly for deposit on an upwardly canted endless belt forming surface. Concurrently, a side stream of the molten material is meltblown and directed in a horizontal direction, by hot high-velocity blasts of gases, onto the forming surface. The downwardly falling coarse and horizontally directed fine fibers intermix on the forming surface, to deposit as a homogeneous nonwoven mixture of the two. The patent discloses that the relatively coarse and relatively fine fiber materials may be different from one another. In another embodiment shown in the patent, in FIGS. 2-3 thereof, coarse fibers are formed in sequential air-blast orifice assemblies longitudinally spaced apart from one another in the direction of translation of the forming surface positioned therebeneath. The forming surface in this embodiment is horizontal; disposed intermediate the respective coarse fiber orifices as a transverse assembly of two restricted orifices associated with means for producing blasts of intensely hot gases therethrough, to form relatively fine fibers. Directly above the forming surface is a shroud which is in fluid flow communication with the orifices generating the respective coarse and fine fibers. The fine and coarse fibers intermingle and mix in the hood, with the mixing augmented by the turbulence of the moving gases therein. In both embodiments a homogeneous mixture of the coarse and fine particles is produced, consistent with the patentee's objective of concomitantly forming and comingling relatively fine and coarse fibers so that the fine fibers tend to pad or cushion the coarse fibers in a manner minimizing inter-abrasion of the fibers, and increasing the insulation value of the composite thereby formed.
U.S. Pat. No. 2,998,051 to K. Sittel discloses a system for forming fibrous articles in which fiber and resin particles are electrostatically combined to form a mat. The system comprises an electrically grounded rotating drum onto which the fiber particles and resin particles are electrostatically collected, with the forming surface disposed between the rotating drum and a pattern electrode disposed therebeneath. A corona electrode initially subjects the fiber particles to a negative electrostatic charge, whicle corona electrodes impose a positive electrostatic charge on the resin particles. The respective resin and fiber particles are then transferred electrostatically to endless conveyor belts from which a reciprocating trolley comprising electrode plates effects transfer of the resin and fiber particles to the rotating drum for deposition on the forming surface in a pattern corresponding to the pattern electrode beneath the forming surface. In this manner, the fiber and resin particles are said to be deposited with maximum intermingling to form a coherent mat. It is stated at column 3, lines 26-27 of the patent that multiple fiber feeds, in the form of spools of yarn, may be fed to the system.
U.S. Pat. No. 3,128,507 to L. E. Pearson relates to a method of making a nonwoven web from two or more tows of filaments. One tow of fibers is fiberized at a first station, which may, for example, comprise a pair of opposedly rotating bladed cylinders, following which the fibers from the first station are transported onto another tow in a randon fashion. The second tow then enters a second station which again may be defined by opposedly or co-directionally rotating bladed cylinders, wherein the first tow fibers are subjected to secondary fiberization concurrently with fiberization of the second tow. The fiberized fibers of the first and second tows then pass from the second station to a laydown surface such as an endless belt conveyor. The patent discloses that the respective tows can be, and preferably are, different as to at least one feature, such as length, color, size, response to heat or other features.
U.S. Pat. No. 3,753,271 to D. M. McBean describes a random web forming machine wherein a fiberizer comprising a toothed cylinder is disposed in a housing to receive a sheet or mat of fibrous raw stock which is fiberized and subsequent thereto delivered to a venturi passage for flow therethrough under negative pressure differential onto a foraminous forming surface. The fiberizer and forming surface are disposed in a housing defining a continous flow system, whereby air flow through the forming surface from the venturi is recirculated through the housing to the mouth of the venturi. The forming surface is an endless belt type, mounted so that the direction of travel of the belt can be adjusted angularly with respect to the venturi discharge duct outlet opening. In such manner differing widths of webs can be produced by varying the direction of travel of the forming surface belt with reference to the discharge opening of the duct.
U.S. Pat. No. 3,781,150 describes a system for producing multilayer fibrous mats, wherein the layers are integrally held together by interfiber bonds at their interfaces under the influence of suction air. A source of pulp fibers is introduced into the system from a shredding unit, it undispersed form, to a disintegrator which produces finely separated short-length fibers. The disintegrator comprises a cylindrical housing containing an axial array of blade runners superimposed upon one another at random angles to form a blade assembly. The blade assembly is disposed in a subhousing formed by a perforated cylindrical wall, through which the disintegrated finely separated short-length fibers are distributed. Air flows into and through the housing by means of an elongate slit communicating with the atmosphere and extending axially on opposite sides of the casing, in association with air intake and damper assemblies at the upper end of the casing. An endless belt foraminous forming surface is disposed beneath the casing to receive fibers passing through the perforated wall under the influence of air flow through the casing and forming surface, to suction boxes disposed beneath the forming surface. A defibrator is associated with the disintegrator to produce long fibers, the defibrator extending substantially the full length of the disintegrator unit. A long-fiber forming lap is defibrated by a toothed wire into finely separated individual fibers which pass through a funnel-like passage axially communicating with a lower portion of the casing, for flow therethrough and deposition on the forming surface. The forming surface is translated in a direction such that long fibers are first deposited on the forming surface followed by fine fibers, and optionally gain by long fibers. The long fibers in this system thus are not produced in the same fiberizer unit as the short fibers, but pass through separate channels in the casing for sequential deposition on the forming surface.
In U.S. Pat. No. 4,268,340 to H. G. Fitzgerald, et al., there is disclosed an apparatus for forming an absorbent web comprising a matrix of hydrophilic and hydrophobic materials derived as wastes in the manufacture of disposable absorbent articles, whereby the waste materials may be recycled and utilized for forming such articles. Alternatively, the feed materials may be virgin hydrophobic and hydrophilic materials. In either event, the feed materials are conveyed to a shredder, comprising a plurality of axially spaced blades mounted on a common shaft, each of the blades having projecting teeth spaced around the periphery of the blades. The resulting shredded material then is air-entrained and conveyed to a cyclone separator, wherein heavier shredded particles are collected and conveyed to a fiberizer, which may be a pin cylinder. The fiberizer reduces the particles passing thereto into a finer size as particles, shreds and fibers, including hydrophilic and hydrophobic material, which then are drawn, via air-entrainment, onto a foraminous forming surface, to provide a nonwoven web comprising such hydrophilic and hydrophobic materials.
U.S. Pat. No. 4,018,646 to A. P. Ruffo, et al., discloses a system which is similar to that of U.S. Pat. No. 3,963,392 to P. K. Goyal, except that only a single pair of fiberizing drums is employed, each associated with the feed of a single component, illustratively described as being pulp on one side and staple fibers on another. A vertically movable baffle is translatable between the respective fiberizing drums to vary the degree of mixing cross-over of the components and produce a variety of nonwoven fabrics, such as a web having a predominance of one fiber type at one of its major faces and a predominance of the other fiber type at the other of its major faces, with a transition between the respective faces in which the predominance of fibers decreases uniformly away from the face at which they predominate. Alternatively, it is possible to form nonwoven webs characterized by essentially discrete layers of the respective components, corresponding to the operation of the apparatus when the central baffle is downwardly most extended.
U.S. Pat. No. 3,952,124 to F. K. Mesek discloses the utilization of dual systems, each of the type as shown in Ruffo, it al., U.S. Pat. No. 4,018,646 to produce a composite multi-layer web therefrom. The dual fiberizer drum assembly having a baffle plate disposed therebetween is utilized to form a first web portion having one face enriched in long fibers and the other enriched in short fibers with the concentration of long and short fibers decreasing substantially uniformly from the enriched faces to form a transition region therein. Similar apparatus is employed to form a second web portion which preferably is the same as the first portion and is bonded thereto in mirror image (back-to-back) relationship, so that the long fiber enriched faces are outwardly disposed to provide substantial structural integrity to the formed web article.
As shown by the foregoing, the art has proposed numerous apparatus and methods for forming integral laid fibrous webs from multiple fiberizable components. These components are either completely intermixed or comingled with one another to produce a substantially homogemeous composition throughout the laid article, or the separate components are laid down in a sequential or partially mixed manner to provide laid fibrous webs with thickness layers of different composition.